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  • #1

    AC to DC for Electric Motor?

    So I want to build a little unit to covert ac to DC to run a motor. I need the convertor to be variable speed as well.

    Details:

    The motor is a treadmill motor. 130vdc 25.4A 3.4 horse motor. I have none of the treadmill controls.

    It will be running off standard 120vac. I will use a bridge rectifier and then use a smoothing cap after that.

    Questions:

    What size rectifier should I use?

    Should I do the variable speed on the ac or the dc side?

    Should I put a regulator on the dc side as well?

    That's all I can think of right niw.
    Nathan
    KD9ARL

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    1978 XS1100E
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    In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

    Theodore Roosevelt
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  • #2
    Just real quick on your needs:
    What size rectifier should I use?
    It should be 30A so you do not stress it.
    Should I do the variable speed on the ac or the dc side?
    I'm not sure what you can find locally. Cheap electronics would make my choice.
    Should I put a regulator on the dc side as well?
    The regulator IS the speed control. You may be able to talk to oregonmotorcycles and see what Tony has to say. I would try and put all the controls on one side or the other, but not split them up.
    Ray Matteis
    KE6NHG
    XS1100 E '78 (winter project)
    XS1100 SF Bob Jones worked on it!

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    • #3
      I kind of figured that if I did the speed control on the dc side it would act as the regulator, just wasn't sure.

      Just haven't been able to find a variable speed 130v dc regulator yet, that isn't $100 +.
      Nathan
      KD9ARL

      μολὼν λαβέ

      1978 XS1100E
      K&N Filter
      #45 pilot Jet, #137.5 Main Jet
      OEM Exhaust
      ATK Fork Brace
      LED Dash lights
      Ammeter, Oil Pressure, Oil Temp, and Volt Meters
      Green Monster Coils
      SS Brake Lines
      Vision 550 Auto Tensioner

      In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

      Theodore Roosevelt

      Comment

      • #4
        Yeah, at the higher amps, the cost goes WAY up! Don't forget you will need a power cord to carry the 20+ amps as well! most wall plugs around the home are 15A, and the 20A that are available need to have a short 12Gauge wire from the panel, or 10gauge wire for longer runs to be safe.
        See if you can find an old beat-up treadmill as a donor. check the dumps, and maybe goodwill.
        Ray Matteis
        KE6NHG
        XS1100 E '78 (winter project)
        XS1100 SF Bob Jones worked on it!

        Comment

        • #5
          I guess I could always go with the simple way of disregarding the regulator and putting the speed control on the ac side. Not really the way I wanted to do it but it will probably be way cheaper.

          Let's see if I can figure out how to build a variable speed dc regulator.
          Nathan
          KD9ARL

          μολὼν λαβέ

          1978 XS1100E
          K&N Filter
          #45 pilot Jet, #137.5 Main Jet
          OEM Exhaust
          ATK Fork Brace
          LED Dash lights
          Ammeter, Oil Pressure, Oil Temp, and Volt Meters
          Green Monster Coils
          SS Brake Lines
          Vision 550 Auto Tensioner

          In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

          Theodore Roosevelt

          Comment

          • #6
            You'll need a step down transformer to bring your AC voltage down to around 91VAC. When rectifying AC, take the rms voltage and multiply times the square root of 2, that will get you your dc voltage out after rectification. Putting a full wave bridge on ac from the wall will get you more like 170 vdc. The lower ac voltage will give you approximately 30% more current output as well. Best do some reading, there's a little more to it than rectify, filter and go. Don't want any XSive's angering the electron gods and getting the "you pissed off Zeus" treatment. Research, experiment, have fun with it in that order. Have a nice day and ride safe
            I am the Lorax, I speak for the Trees

            '80 XS1100 SG (It's Evil, Wicked, Mean & Nasty)

            '79 XS1100 F R (IL Barrachino)

            '00 Suzuki Intruder 1400 (La Soccola)

            '77 KZ400s (La Putana)

            Comment

            • #7
              I'm assuming this is a permanent-magnet motor? If it's a 'universal' motor, you can run it on AC.

              If it is DC-only, rather than using large single diodes for each 'bridge' in the rectifier, I think I'd go with multiple diodes in parallel and shoot for at least a 50 amp total rating to cover current inrush and low speed/high load situations.

              If you're trying to easy/lo-buck the speed control, a rotary resistor (if you can find one big enough) on the AC side would probably be easiest short of finding a control out of another treadmill. If you use a step-down transformer before the rectifier, that should reduce the input current enough that you could get away with using a 2000W lighting dimmer.
              Fast, Cheap, Reliable... Pick any two

              '78E original owner - resto project
              '78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
              '82 XJ rebuild project
              '80SG restified, red SOLD
              '79F parts...
              '81H more parts...

              Other current bikes:
              '93 XL1200 Anniversary Sportster 85RWHP
              '86 XL883/1200 Chopper
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              Yep, can't leave nuthin' alone...

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              • #8
                Honestly I would never be running it anywhere close to full speed anyways and that is one of the reasons I am not super worried about the max voltage. I wouldnt be able to run it more than 50% for the needed rpms for my use.
                Nathan
                KD9ARL

                μολὼν λαβέ

                1978 XS1100E
                K&N Filter
                #45 pilot Jet, #137.5 Main Jet
                OEM Exhaust
                ATK Fork Brace
                LED Dash lights
                Ammeter, Oil Pressure, Oil Temp, and Volt Meters
                Green Monster Coils
                SS Brake Lines
                Vision 550 Auto Tensioner

                In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

                Theodore Roosevelt

                Comment

                • #9
                  I would suggest regulating the AC. Using a standard rheostat before rectifying will keep voltage and current way down to a more manageable level. Especially since you won't be cranking the guts out of it constantly. I'd try looking into the giant rectifier packs used in the 120-150+ amp alternators, cheap and everywhere! Regulating DC would keep the rectifiers full throttle smoothing the full wall AC even though you won't be using it all, all the time. No sense loading the rectifiers constantly. Not to mention DC regulators for that much current can get pricey. Regulate the AC, the circuit will only be subjected to what voltage you " let in" through regulating...a much happier AC-DC circuit. Just my $0.02
                  Matt
                  81H Rebirth/Custom Build
                  1st Gen RX7; Audi quattro; Wrangler JK
                  PanikSwitch Cycles - Brewer ME
                  http://s48.photobucket.com/user/Arth...201100%20Build

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